Why does a cannon recoil / jump more the hotter the barrel gets?

[Thunderbird]

Want to settle a debate about old-style naval gunnery.

 

Why does a cannon recoil / jump more the hotter the barrel gets?

 

Is this true and if so, what's the reason?

[Medic1281]

At a guess could it be that as the barrel gets warm, the metal expands and reduces the bore, hence increasing pressures and recoil?

[Hamster]

IF it's true, and I have to say I'd never heard of this before, it may have something to do with the nature of the propellant being able to burn more efficiently in a hotter barrel thus creating more thrust which would result in more recoil.

 

Cannons deployed on land may look as thought they're producing more and more recoil perhaps because the wheels create a more defined recoil channel the more they're shot?

[Thunderbird]

It's to do with the Patrick O'Brian books, he often mentions the cannons skipping about with more recoil as they get hot, I did think it must be something to do with expansion and a tighter fit with the ball.

[lakeside1000]

simple, for every action there is a reaction, cannon ball goes one way cannon the other,when cold the bore tolerance is very loose, so gas escapes around the ball even with good wadding, the ball has less contact with the barrel and gets away quickly, but once the barrel begins to warm up, it expands ,closing the gap between the ball and barrel, this means more efficient pressure containment behind the ball, increasing the muzzle velocity but also increasing the amount of reaction back into the cannon, in the days when they were used to fight sea battles, sailors would cool the barrels with buckets of water to reduce the risk of the ball actually becoming jammed in the barrel and causing the barrel to explode with pretty devasting results.

[Thunderbird]

I like that, reckon you're right. Thanks guys.

[Hamster]

simple, for every action there is a reaction, cannon ball goes one way cannon the other,when cold the bore tolerance is very loose, so gas escapes around the ball even with good wadding, the ball has less contact with the barrel and gets away quickly, but once the barrel begins to warm up, it expands ,closing the gap between the ball and barrel, this means more efficient pressure containment behind the ball, increasing the muzzle velocity but also increasing the amount of reaction back into the cannon, in the days when they were used to fight sea battles, sailors would cool the barrels with buckets of water to reduce the risk of the ball actually becoming jammed in the barrel and causing the barrel to explode with pretty devasting results.

 

Sounds very plausible, as you say it is the gases escaping initially causing lower velocity and progressively getting more efficient as the bore/ball gap optimises with expansion.

[aister]

Could the barrel fowling up with black powder crud also tighten it up too? Just remembering what a workmate said about his muzzle loading .577, the dirtier it got the harder it was to push the ball home and the stiffer the recoil became.

[TIGHTCHOKE]

simple, for every action there is a reaction, cannon ball goes one way cannon the other,when cold the bore tolerance is very loose, so gas escapes around the ball even with good wadding, the ball has less contact with the barrel and gets away quickly, but once the barrel begins to warm up, it expands ,closing the gap between the ball and barrel, this means more efficient pressure containment behind the ball, increasing the muzzle velocity but also increasing the amount of reaction back into the cannon, in the days when they were used to fight sea battles, sailors would cool the barrels with buckets of water to reduce the risk of the ball actually becoming jammed in the barrel and causing the barrel to explode with pretty devasting results.

 

 

Both barrel and shot will get to similar temperatures and both will expand to a degree!

 

The barrels were wetted to prevent any burning powder residue from igniting the fresh charge being rammed in before the ball!

[Kes]

Add to the thoughts that they used to fire red-hot shot to set fire to ships - did the gunnery charts show that would fly further ? if so then the expansion theory is probably the correct one.

[ferguson_tom]

 

 

Both barrel and shot will get to similar temperatures and both will expand to a degree!

 

The shot wont get to a similar temperature to the barrel its only in there a short time so wont conduct the heat quick enough to make them similar.

Edited June 26, 2013 by ferguson_tom

[al4x]

since when did a barrel that expanded actually contract as per the theory above

[Guest cookoff013]

of it gets too hot, wouldnt it cookoff?

[Troosers Too]

since when did a barrel that expanded actually contract as per the theory above

Presumably the theory suggests that the steel the barrel is made of would expand in all directions, meaning that the bore would become smaller at the same time as the overall external dimensions of the barrel would become larger.

 

I'm no engineer so I'll be the first to accept that the truth from one.

 

TT

[mudpatten]

In the heat of battle the gun was cooled and made ready to safely accept the next bagged charge using a sheepskin swab soaked in water. It was`nt just damp, it was wringing wet. The heat from the gun would almost instantly evaporate the water in the barrel, whilst the outside of the barrel would frequently be treated to a bucket of water. The dangers of cooking off a charge with an overheated gun were very real. Lets remember that the charge for some of the old m/l smoothbore ships cannon was in excess of 10 pounds of powder. With the arrival of rifled muzzle loaders this became even larger.

 

A large punt gun, by way of comparison, would rarely use more than 4 ounces of the same very coarse grain black powder.

 

I must say that I have not heard of a cannon`s recoil increasing the more it`s fired. Significant steps were taken to prevent overheating and these same steps, wet-swabbing the bore, would have removed much of the powder fouling so it`s hard to see how that could be a cause.

 

The shot would rarely have been dropped straight onto the powder charge because of "windage", the space between the ball and the barrel, which made loading easy. A ball would, for safety reasons be seated with the ramrod, but, since it was a relatively loose fit it would not need to be hammered home forcibly. It would sit atop a main driving wad of rag, old rope, caulking oakum etc, or upon a purpose made wooden sabot, so although the ball was sitting in a hot environment- the bore of the gun- much of its surface would not in fact be in contact with the barrel wall and therefore not subject to the same conducted heat transfer as would have been the case were it a tight fit.

 

I`m intrigued by this suggestion and I`ll see if I can locate an expert on old Naval cannon in Portsmouth Dockyard and see what they have to say.

[TIGHTCHOKE]

Looking forward to any light you can throw on this question M.P.

[Thunderbird]

Me too guys, thanks for the reply.

 

By the way I highly recommend the Patrick O'Brian novels. Brilliant stuff and they get better with re-visiting.

[henry d]

"2-6 Heave!"

[mudpatten]

The more I think about the original question, the less likely it actually seems.

 

i did wonder, as Henry suggests, if it might have been something to do with the rope breaching. Controlling the recoil on a naval cannon relies on a number of factors. Not least the weight of the gun, the geometry of the gun carriage and the effectiveness of the rope breaching.

 

It would seem reasonable that,during a period of frenetic use the breaching rope, and indeed all the ropes associated with working the gun, might stretch. This would cause the gun to run back further, but would not make it jump any more than when the ropes were unstretched.

 

Some years ago I took part in some pattern testing of a number of punt guns. Admittedly not as large as a cannon, but the principles should have been the same. Both breach and muzzle loaders were tested, especially one breach loader which was fired five times in relatively quick succession. The barrel was certainly hotter than usual and the bore was only rodded out with an oily rag between shots rather than wet swabbed. I have no recollection, nor does anyone else who took part of any increase in recoil.

 

If I have no success with an accurate answer from the technical staff on board HMS Victory or the Warrior, I`ll take a run up to the Tower Armouries national artillery museum which is just behind me.

[TIGHTCHOKE]

I'm very sceptical in relation to the Lakesides conclusions!

Edited June 26, 2013 by TIGHTCHOKE

[deershooter]

When I went to school and you heated up a cylinder the internal bore got larger not smaller its called expansion you have to cool it to contract it

 

:exclamation: :stupid:

 

Deershooter

[JonathanL]

since when did a barrel that expanded actually contract as per the theory above

 

This is what I thought. I was always under the impression that if your heated a piece of metal with a hole in it then the hole gets bigger. When you are heat shrinking a pin into a piece of metal you heat the pice of metal (so that the hole expands) and cool the pin (so that it contracts). You hammer the pin in and the metal contracts around the pin as it cools, the pin expands as it warms creating a very firm grip. I believe this is how Steyr Mannlicher fit their barrels - at least in the SSG.

 

J.

[Troosers Too]

Now then, I've just broken one of my life's rules and sought out an engineer (they're a funny lot aren't they?) who tells me that since the cannon would heat up from the bore outwards, the bore would actually get smaller to begin with as the outside of the gun is considerably cooler than the centre.

 

 

I don't really know why I'm getting involved with this - it's a bit like a golfish getting involved in a discussion about hang gliding.

 

Cheers

TT

[Dekers]

Now then, I've just broken one of my life's rules and sought out an engineer (they're a funny lot aren't they?) who tells me that since the cannon would heat up from the bore outwards, the bore would actually get smaller to begin with as the outside of the gun is considerably cooler than the centre.

 

 

I don't really know why I'm getting involved with this - it's a bit like a golfish getting involved in a discussion about hang gliding.

 

Cheers

TT

 

I've never heard of this cannon business, but not had much involvement with cannons over the years.

 

The above makes sense!

[henry d]

OK a bit of a think and a read and some more thinking...

 

Barrels are mopped between shots to stop powder from pre-igniting and therefore cools the internals of the barrel and gets it close to original diameter. Wads are, generally, placed fore and aft of projectile so pressure escaping is minimal and projectiles were loose fit. Due to the barrel being hot the temperature must rise in the bore somewhat and using the combination gas laws P1 V1/T1 = P2 v2/T2 volume will decrease by a small amount as bore tightens with heat, but temperature increases quite a bit, so they may cancel each other out to some extent. Secondary, possibly more importantly, the temperature has a big bearing on the powder ignition and will ignite faster as the barrel warms up which will increase pressure and therefore recoil. F=MA if I remember correctly, the mass of the cannonball is similar but acceleration increases due to hot powder, so force felt/seen increases.

 

All schoolboy physics and I realise from wiki etc that there is a lot of other complicated laws involved here, but just my take on things.